Aptitude - Problems on Trains - Discussion

Speed 60 km/hr.
Time = 9 sec.

1. Convert speed into m/sec.
ie, Speed/3.6 => 60/3.6=16.67 m/sec.

2. To find the length.
Length L =Speed x time.
ie, L= 16.67 x 9 =150.
So the length of the train is 150 m.

Length of train = speed * time.
= 9 * 60 * 5/18(converting km/hr into m/sec).
= 150 meters.

Q. Sonali invests 15% of her monthly salary in insurance policies. She spends 55% of her monthly salary in shopping and on household expenses. She saves the remaining amount of Rs. 12,750. What is Sonali's monthly income?

Solution:

Let the monthly-salary be X.

Total %-of-amount spent = (15 + 55) = 70% of X.

Remaining amount saved is 30% of X.

Now, 30% of X = 12750. Then 100% of X = ?

X = (12750/30) x 100 = 42,500.

Required answer X = Rs. 42,500. //

Note:-

Amount Spent in Insurance (15% of X) = (15/100) x 42500 = Rs. 6,375.
Amount Spent in Shopping (55% of X) = (55/100) x 42500 = Rs. 23,375.
Amount Saved (30% of X) = (30/100) x 42500 = Rs. 12,750.

Monthly Salary = Rs. (6375 + 23375 + 12750) = Rs. 42,500.

How is it possible? Please explain to me.

The speed of train in 1sec =(60*5)/18=16.66666666666667 m/sec,
As we know that an object or a thing can be crossed with the length of a train
we took 9sec then
The length of train = 16.66666666666667 * 9 = 150 m.

60 * 60 = 3600,
1000/3600 = 5/18,
60Km/hr.
1km = 1000m,
1hr = 60min.
1sec = 60sec.

Thanks all for giving a clear explanation.

@All.

Here's my explanation:

1. You have to convert speed km/h into m/s.
And the formula to convert speed km/h into m/s is 60 x 5/18 (Note : 5/18 is a constant).
Speed = 16.67 m/s.

2. Distance = speed X time.
16.67 x 9 = 150m is the length of the train.

600 % 36 = 16.67.
16.67 * 9 = 150.

Time = Length of the train/Speed of the train.
Time is in seconds, do speed should be in metres/Seconds.
60 km/hr = 60 × 5/18 m/s = 50/3 m/s.
9 seconds = length/50/3.
9 × 50/3 = length.
length = 3 × 50 = 150 metre.